/* namespacing object */
var net=new Object();

net.READY_STATE_UNINITIALIZED=0;
net.READY_STATE_LOADING=1;
net.READY_STATE_LOADED=2;
net.READY_STATE_INTERACTIVE=3;
net.READY_STATE_COMPLETE=4;
/*--- content loader object for cross-browser requests ---*/
net.ContentLoader=function(url,on_load,on_error,method,params,contentType){			//ContentLoader会实例化，this指向实例化对象
  this.req=null;
  this.on_load=on_load;
  this.on_error=(on_error) ? on_error : this.defaultError;
  this.loadXMLDoc(url,method,params,contentType);
}
//////ContentLoader   定义------------------------------/>


net.ContentLoader.prototype.loadXMLDoc=function(url,method,params,contentType){
  if (!method)   //method默认是get
  {
method="GET";
  }
  
  if (!contentType && method=="POST")
  {
contentType='application/x-www-form-urlencoded';
  }
  /////////////一下是实例化request，跨浏览器
  if (window.XMLHttpRequest)
  {
this.req=new XMLHttpRequest();
  }
  else if (window.ActiveXObject)
  {
  //add try catch;
  try {
    this.req = new ActiveXObject("Msxml2.XMLHTTP");
  }catch (e1){
    try {
    this.req = new ActiveXObject("Microsoft.XMLHTTP");   
    } catch (e2){
  }
  }
    //
//this.req=new ActiveXObject("Microsoft.XMLHTTP");
  }
  ///以上是实例化request  跨浏览器
  
  if (this.req)
  {
try
{
  var loader=this;
  this.req.onreadystatechange=function()  //注册
  {
  net.ContentLoader.onReadyState.call(loader);//loader是ContentLoader实例化对象
  }
  this.req.open(method,url,true);
  if (contentType)
  {
  this.req.setRequestHeader('Content-Type', contentType);
  }
  this.req.send(params);
}
catch (err)
{
  this.on_error.call(this);
}
  }
}////END  loadXMLDoc/////////////////


net.ContentLoader.onReadyState=function(){
  var req=this.req;
  var ready=req.readyState;
  if (ready==net.READY_STATE_COMPLETE){
var httpStatus=req.status;
if (httpStatus==200 || httpStatus==0){
  this.on_load.call(this);
}else{
  this.on_error.call(this);
}
  }
}
net.ContentLoader.prototype.defaultError=function(){
  alert("error fetching data!"
+"\n\nreadyState:"+this.req.readyState
+"\nstatus: "+this.req.status
+"\nheaders: "+this.req.getAllResponseHeaders());
} 

